FR2593166A1 - PROCESS FOR PRODUCING A METAL OXIDE POWDER FOR CERAMIC MATERIALS AND ZIRCONIA POWDER OBTAINED THEREBY - Google Patents

Abstract

Process for the manufacture of a metal oxide powder for ceramic materials by the hydrolysis of a metal alcoholate in the presence of an acidic organic compound. The process applies to the production of metal oxide powders, such as zirconia powders, with a mean particle diameter of between 0.05 and 2 microns.

Description

2593 1 66

  -1 - Process for producing a metal oxide powder for ceramic materials and zirconia powder obtained by this process

  The invention relates to the manufacture of ceramic materials.

  It relates more particularly to a process for the manufacture of metal oxide powders intended for the implementation of

ceramic materials.

  A process is known for the manufacture of an alumina powder, according to which an aluminum alkoxide is hydrolyzed in the presence of an excess of water, an aqueous suspension of aluminate is collected which is subjected to an operation. peptization by addition of acid, and the peptized suspension is poured dropwise in a hydrocarbon

liquid.

  This known process has the disadvantage of a great complexity, inherent in particular to the operations of peptization and flow, drop by drop through a hydrocarbon bath, which require

  in addition to intermediate operations - filtration and rissage.

  The invention aims to remedy this drawback by providing a simplified method for the manufacture of metal oxide powders for ceramic materials, by hydrolysis of metal alkoxides, this process no longer requiring the operations of peptization and

  transfer in a hydrocarbon bath.

  Accordingly, the invention relates to a method for producing a metal oxide powder for ceramic materials, by hydrolysis of a metal alkoxide, wherein the hydrolysis is

  operated in the presence of an acidic organic compound.

  In the context of the invention, the term "ceramic materials" is intended to denote inorganic non-metallic materials, the use of which, starting from a powder, requires high temperature treatments, such as melting or sintering treatments. -

  (P. William Lee - "Ceramics" - 1961 - Reinhold Publishing Corp. -

  page 1; Kirk Othmer Encyclopedia of Chemical Technology - Third Edition Volume 5 - 1979; John Wiley & Sons, USA - pages 234-236:

"Ceramics, scope").

  In the process according to the invention, the metal alcoholate

  means any compound in which a metal is connected through

  of an oxygen atom, to a hydrocarbon group such as an aromatic group or a linear aliphatic group or

  cyclic, saturated or unsaturated, unsubstituted or partially substituted

  completely or totally. Aliphatic alcoholates with aliphatic groups

  ticks are especially recommended; those with aliphatic groupings

  Unsubstituted saturated solvents are preferred, such as, for example, methyl, ethyl, n-propyl iso-propyl, n-butyl and iso-butyl groups. The function of hydrolysis is to decompose the alkoxide with water to produce the hydrated metal oxide and an alcohol. Although one can work indifferently with an excess or a defect of water compared to the quantity strictly necessary to decompose all of the alkoxide, it is desirable that the quantity of water used is at least equal to the amount

strictly necessary.

  According to the invention, the hydrolysis is carried out in the presence of a

acidic organic compound.

  By acidic organic compound is meant any organic compound which has an acid character. Saturated and unsaturated carboxylic acids and their derivatives are especially recommended; carboxylic acids containing more than three carbon atoms in their molecule and derivatives of these acids are preferred. Carboxylic acids which have proved to be especially advantageous are those containing at least eight carbon atoms in their molecule, such as octanoic, lauric, palmitic, isopalmitic, oleic and stearic acids. Examples of organic acid derivatives which can be used in the process according to the invention are the

  anhydrides, esters and salts of these acids.

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  The optimum quantity of acidic organic compound to be used depends both on the selected acidic compound and on the metal alkoxide used, and it must be determined in each particular case according to the quality sought for the morphology. ceramic powder. In general, it is necessary to achieve a molar ratio between the acidic organic compound and the metal alkoxide at least equal to 10-3; in the case of a carboxylic acid, preferred molar ratios are those between 0.005 and 3; molar ratios between 0.015 and 0.35

are good.

  In a specially recommended embodiment of the process according to the invention, the acidic organic compound is mixed with the metal alkoxide before hydrolysis. This embodiment of the invention ensures the production of a metal oxide powder of narrow granulometry, whose grains are regular, substantially

  spherical, and it reduces the risk of agglomerates formation.

  To further improve the quality of the powder, in particular to reduce the risks of formation of agglomerates and to improve the sphericity of the grains, the alcoholate and the water are advantageously used in the form of organic solutions. If appropriate, it is appropriate that the organic solvent of the alcoholate is free of water. It is possible to use identical or different organic solvents for the alcoholate, on the one hand, and for water, on the other hand. In the case where the alcoholate and the water are dissolved in different organic solvents, it is generally appropriate to choose miscible organic solvents. Alcohols and their derivatives are generally suitable, especially methanol, ethanol,

  n-propanol, iso-propanol, n-butanol and iso-butanol.

  The optimum dilution ratios of the alcoholate and water in their respective organic solvents depend on various factors, including the alkoxide used, the amount and nature of the selected acidic organic compound, work, the turbulence rate of the reaction medium and the desired quality for the metal oxide powder; they must be determined in each particular case by laboratory routine work. As a rule, it is recommended that the organic solution of the alcoholate and the organic water solution respectively contain less than 2 moles of metal alkoxide per liter and less than 5 moles of water per liter. Especially advantageous molar concentrations are those between 0.05 and 1 for the metal alkoxide solution and between 0.1 and 3 for

the organic solution of water.

  Hydrolysis can be carried out in the ambient air. To avoid the risk of an uncontrolled decomposition of the metal alkoxide, it is possible, according to a particular embodiment of the process according to the invention, to carry out the hydrolysis under a gaseous atmosphere that is free from moisture. Dry air, dehydrated air, nitrogen and argon are examples of atmospheres that can be used in this

  embodiment of the invention.

  In principle, temperature and pressure are not critical.

  c. In general, in the majority of cases, we can work on the

  room temperature and normal atmospheric pressure.

  The metal oxide obtained at the end of the process according to the invention

  tion is in the form of a powder of fine particles generally

  spherical, with a diameter not exceeding 5 microns,

  usually between 0.05 and 2 microns.

  The powder may optionally be dried and heat treated at an appropriate temperature to remove the compound

  organic acid, water and the organic solvents that permeate it.

  Heat treatment can be set to control porosity

or eliminate it completely.

  The process according to the invention finds an interesting application for the production of metal oxide powders of groups III and IV of the periodic table of the elements, by hydrolysis of alkoxides of these metals; it finds a particularly advantageous application for the production of zirconia powders by hydrolysis

of zirconium alkoxide.

  The invention therefore also relates to zirconia powders

  obtained by the process according to the invention, formed of spherical grains

  whose diameter does not exceed 5 microns and is preferably

between 0.05 and 2 microns.

2 5 9 3 1 6 6

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  The few examples described below are used to

  illustrate the invention. These examples are given with reference to the appended figures which are eight photographic reproductions of zirconia powders, at a magnification of 20,000 X. The examples relate to tests for the production of zirconia powders according to the following operating process, according to the invention. In a reaction chamber maintained under an anhydrous nitrogen atmosphere at a temperature of 25 ° C, an organic solution of a zirconium alkoxide and a determined amount of carboxylic acid was used and the resulting mixture was subjected to moderate agitation for about ten minutes. Then, while maintaining the mixture under vigorous stirring, a defined amount of an organic water solution was added at once and the reaction mixture was milled for 2 hours. After ripening, the reaction mixture was subjected to centrifugation and the zirconia powder was collected which was washed with anhydrous ethanol and dried with a current

air at room temperature.

  In the examples, the average powder diameter was calculated from measurements on photographic reproductions, the

  mean diameter being defined by the following relation (G. HERDAN -

  "Small particle statistics" - 2nd edition - 1960 - Butterworths -

pages 10 and 11): -

n nidi d = _ni

  o denotes the number of particles of diameter d ..

Example 1

  This example is characterized by the following specific operating conditions:

  - organic solution of zirconium alkoxide: 100 ml of a solution

  0.2 M zirconium n-butoxide in ethanol; Carboxylic acid: 1.6 × 10 -3 mole of oleic acid; - organic solution of water: 100 ml of a 0.7 M solution of water in

ethanol.

  The zirconia powder obtained is shown in FIG.

  It has an average particle diameter of 0.59 microns.

Examples 2 to 4

  These examples differ from Example 1 only by the selection of the carboxylic acid, which was: - octanoic acid (example 2) lauric acid (example 3) - isopalmitic acid (example 4) Average particle diameters of the zirconia powders obtained for each test are listed in the following table. The

  Figures 2 to 4 show samples of these powders.

  EXAMPLES 5 AND 6 These examples are distinguished from Example 1 only by the amount of oleic acid used, which was: Example 5: 0.96 × 10 -3 mole;

Example 6: 3.16 x 10 -3 mol.

  Figures 5 and 6 show samples of powders obtained

  The powders were characterized by an average particle diameter of: Average diameter Example Particle acid Figure No. (micron) No. 2 octane; 0.35 2 3 lauric 0.49 3 4 isopalmitic 0.58 4 -7- Example 5: 0.46 micron;

Example 6: 1.20 microns.

Example 7

  This example differs from Example 1 in the selection of the alkoxide, which was zirconium n-propoxide. All the

  other conditions remained unchanged. -

  Figure 7 shows a sample of the zirconia powder obtained. This had a mean particle diameter of

0.70 micron.

Example 8

  This example is characterized by the following operating parameters:

  - organic solution of zirconium alkoxide: 100 ml of a solution

  0.2 M zirconium n-propoxide in n-propanol; carboxylic acid: 3.2 × 10 -3 mole of oleic acid; - organic solution of water: 100 ml of a 0.7 M solution of water in

n-propanol.

  The zirconia powder obtained is represented in FIG. 8.

  It had an average particle diameter of 1.5 microns.

Example 9

  This example is characterized by the following operating conditions:

  - organic solution of zirconium alkoxide: 100 ml of a solution

  0.2 M zirconium n-butoxide in n-butanol; Carboxylic acid: 6.4 × 10 mole of oleic acid; organic solution of water: 100 ml of a 0.7M solution of n-butanol water. The zirconia powder obtained had a mean diameter of

particles equal to 2.6 microns.

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R E V E N D I CATIO NS

  1 - Process for producing a metal oxide powder for ceramic materials, by hydrolysis of a metal alkoxide, characterized in that the hydrolysis is carried out in the presence of an acidic organic compound. Process according to Claim 1, characterized in that

  selects the acidic organic compound from the carboxylic acids

  containing more than three carbon atoms in their molecule

and derivatives of these acids.

  3 - Process according to claim 1 or 2, characterized in that the acidic organic compound is used in a molar amount of between 0.005 and 3 times the molar amount of

the metal alkoxide.

  4 - Process according to any one of claims 1 to 3,

  characterized in that the acidic organic compound is added to

  the metal alkoxide, before hydrolysis.

  - Process according to claim 4, characterized in that, to hydrolyze the metal alkoxide, an organic solution of said alkoxide containing the acidic organic compound is mixed,

with an organic solution of water.

  6 - Process according to claim 5, characterized in that it implements an alcoholic solution of the alcoholate, containing between 0.05 and 1 mole of alcoholate per liter and an alcoholic solution

  of water containing between 0.1 and 3 moles of water per liter.

  7 - Process according to any one of claims 1 to 6,

  characterized by selecting the metal alcoholate from

  alcoholates of Group III and IV metals in the periodic table

only elements.

  8 - Process according to claim 7, characterized in that

  the metal alkoxide is zirconium alkoxide.

  9 - Zirconia powder obtained by a process according to one of

  any of claims 1 to 8 formed of spherical grains

  whose diameter is between 0.05 and 2 microns.